GB748821A - Improvements in and relating to television cameras - Google Patents

Abstract

748,821. Television. BRITISH BROADCASTING CORPORATION. Oct. 1, 1951 [Sept. 29, 1950], No. 23950/50. Class 40 (3). In television apparatus for generating a composite signal as described in Specification 743,402 whereby at a receiver there is produced a picture in which part of an image viewed by a first camera is replaced by an image viewed by a second camera, the necessary switching of the two cameras being effected by control pulses generated by a photo-electric cell viewing. an unmodulated raster through a mask having a profile corresponding to said part of the image viewed by the first camera, means are provided for coupling the two cameras and the assembly of mask and raster whereby movement of one camera is automatically followed by a corresponding movement of the other and a corresponding change in the relative sizes and/or relative positions of the mask and raster. When the first camera executes a tracking movement, the corresponding movement of the second camera is similar, and the size of mask relatively to that of the raster as seen by the photoelectric cell is increased and reduced respectively as the camera moves backwards and forwards. This latter change is effected either by movement of the mask or by change in the size of the raster. When movement of the first camera is a tilting or panning movement, the second camera makes a similar movement and a change is made in the vertical and horizontal direction of the relative, position of mask and raster, either mechanically, by movement of the mask, or electrically, by movement of the raster. The necessary movements and changes in the relative sizes and/or positions depend upon the angles of the two camera lenses and the scale of the two images viewed by the cameras. Fig. 1 illustrates a servo system for controlling the two camera tracking movements. The first camera 17 unbalances the bridge circuit by variation of resistor 10 and an amplifier 16 responsive to the unbalance voltage controls a motor 18 to effect a corresponding movement of the second camera 19 until balance is re-established by resistor 11. The degree of movement of the second camera may be varied by adjusting resistors 12 and 13. Similar servo systems control the tilting and panning movements, and may also control the position of the mask. Alternatively the raster may be shifted by the arrangement shown in Fig. 2 in which a variable direct current is passed into the deflection coils by triode 23 under control of potentiometer 24 mechanically coupled to the first camera. Changes in the size of the raster in response to the tracking movement of the first camera may be effected by controlling the gain of the scanning amplifiers by a voltage developed by a potentiometer coupled to the wheels of the camera dolly. Specification 672,895, [Group XXXVIII], is referred to in the Provisional Specification.